Don't guess. uBO comes with a dashboard just like uM did that shows you exactly what's being blocked. It's usually very obvious what important script is being blocked whose domain you need to allow, what PUA symbols font is being blocked, etc.
>take minutes, possibly large fractions of an hour
Switching to the other window where you have the uBO list open and copy-pasting a line takes about as long as clicking the uM browser button, eyeballing the table and finding the right cell to click.
Your initial setup is going to take long. After that you'll a) get better at it, and b) you won't need to update it as often. I started doing this two years ago and these days I edit less than 2 lines per month on average. My list has rules for ~80 domains and is ~400 lines long, not counting whitespace and comments.
In any case, I'm not trying to convince you. I keep seeing people thinking that uBO can't do things that uM can, so I post that link to let them know that it can do those things except for cookies. Whether you want to use that info, or you think it's not worth it and you want to keep using uM, is something you decide for yourself.
